How to use a Tach Dwell Meter

A dwell meter is used to check the dwell angle on vehicles with a points-type ignition. Dwell angle is the length of time (measured by the degree of rotation of the distributor cam) the contact points open on a points-type ignition system. Points-type ignition systems were commonly used on vehicles manufactured before the mid-1970s. The dwell angle must be periodically checked on these vehicles to ensure proper operation of the ignition system. In addition, the dwell angle on these vehicles must be checked before setting the ignition timing.